pressure dropping on my baxi combi instant 80he?

First check it's not the PRV (safety valve) leaking, they can after a while - next, as "erg" suggests, you have a leak and must find it - it may be hidden under floor or even a rusted radiator, but you would see that -continually topping up will lead to serious probs., scaling- up etc

Big L
November 2009

there is a leak somewhere,

erj
November 2009